#include <iostream>
#include <cstdio>
using namespace std;

typedef long long LL;

const int N = 55;

LL n, arr[N];

int main()
{
	cin >> n;
	
	arr[1] = arr[2] = 1;
	
	for (int i = 3; i <= n; i++)
		arr[i] = arr[i - 1] + arr[i - 2];

	cout << arr[n] << ".00\n";
	
	return 0;
}
